2015年9月23日 星期三

9.23 Stuck with left/right handed orientation

http://www.grahamwideman.com/gw/brain/orientation/orientterms.htmToday I am stuck at this issue.

http://atonal.ucdavis.edu/lab_howto/fmri/image_orient_display.htm
has some nice diagram showing neurological and radiological orientation.

RadiologicaL (Right is Left)
NeurologicaL (Right is Not Left)

Be careful when I need to switch label (quoted from FSL forum):

Hi,

Why do you want to do this?

The use of labels is to enable people to rearrange their
data into different views, as seen by FSLView.  But the
RL and LR change does not change anything for FSLView,
which always shows things with a consistent "handedness"
which is based on the same one as used by the template
images, shown as "radiological".  You can change the
left-right order if you really want, but there is no real need
to do that with the current version of FSL.  If you do it, it will
change your storage between the "radiological" and "neurological"
conventions.  We explicitly stop this happening when using
the labels with fslswapdim in order to avoid this happening
as an unintentional side-effect.

So I simply recommend that you don't do this.
If you really want to _only_ swap LR, then you need to use the
"-x y z" syntax _and_ use fslorient -swaporient, to make sure
that the relationship between the data and the labels stays
consistent.  If you do not run both commands then the left
and right labels will get mixed up with respect to what is
contained in the brain image which is bad.

Hope this makes it clearer.
All the best,
    Mark

2015年9月16日 星期三

9.16 New questions

How to perform statistics on longitudinal data, for paired or unpaired test?
How to analyze the data, in the whole ROI or in clusters?

2015年9月2日 星期三

9.2 Why a paired test is better than unpaired

Because you always groups things by observation. You assume the difference is due to the observation, but there may be confounders that you simply has not observed. The observation can be randomly perceiving only one factor but ignore other factors. Things are related, that one factor may change other factors therefore affect the subject. To control other factors, the best thing can do is use the same subject and control its environment, giving one factor (that one can perceive as one factor) at a time.